This invention relates generally to exhaust gas recirculation (EGR) valves and more specifically to such valves which are electrically actuated.
An exhaust gas recirculation valve is common place in the pollution control system of automotive engines. The EGR valve recirculates a predetermined amount of exhaust gas from the exhaust system to the intake manifold. Prior EGR valves relied upon vacuum motors for actuation. Such vacuum actuation provided for the continuous movement of an armature or closure member relative to a valve seat. A deficiency in the vacuum operated EGR valves is that sufficient vacuum force is not always available during needed periods of operation. Later versions of EGR valves contemplated replacing the vacuum motor with a variety of electrical actuators such as a stepper motor. A goal of electronically controlled EGR valves is to meet the continuous performance characteristics of the vacuum actuated valves. As such, a stepper motor having many poles is used to approximate the resolution of the vacuum activated EGR's, however, the increased number of poles increases the cost of the device. Another inherent shortcoming of the stepper motor or of a DC motor controlled EGR valve is in its failsafe mode of operation. It is desirable that upon electronic failure, the EGR valve should remain closed. This is difficult to achieve in the stepper or DC motor EGR valve since the position of the closure element is often established by a lead screw and nut which is driven by the motor and as such, the lead screw and nut may rest in an intermediate position at the time of failure of the motor. Another variety of electrically operated EGR valve is that type of valve which utilizes solenoids. To achieve adequate resolution can require using a plurality of such solenoids which increases the complexity and cost of the system. Typically the solenoid controlled EGR valve is constructed such that in the absence of an electrical signal a spring biases the closure member against a valve seat. As such, the closure element is maintained at its largest air gap. The solenoid can only provide the minimum available force when the closure member is against the valve seat and therefore it cannot precisely control the flow rate through the EGR valve when it is most crucially needed. Further, linear solenoids have a greater out of balance force resulting from a relatively heavy armature supported against a spring. Consequently, the linear armature is more difficult to control when subjected to high vibrational forces.
It is an object of the present invention to provide an EGR valve having high resolution at smaller valve openings than at larger valve openings. A further object of the present invention is to provide precise EGR control at low engine speeds. A further object of the present invention is to provide an EGR valve that is controllable in a position measurement and in a differential pressure mode of operation.
Accordingly, the invention comprises: a valve comprising:
a valve stem, eccentrically positioned from an axis of rotation and movable in a substantially axial manner relative to a valve seat; means carried by the valve stem for closing the valve seat; a first shaft eccentrically positioned relative to the axis of rotation and engagably connected to one end of the valve stem, and means for rotating the first shaft about the axis to cause the valve stem to move axially.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.